Over the past few decades, telecommunications and Internet have experienced an incredible growth and expansion. Technologies have changed from centralized computing to personalized computing and now to mobile computing with a convergence of networks, devices and services.
Mobile computing is made possible through the use of Mobile Internet Protocol (IP) or more specifically Mobile IPv6 (MIPv6), using the version 6 of IP. Mobile IPv6 (MIPv6) is an Internet Engineering Task Force (IETF) standard communication protocol. It has been designed to allow mobile users to move from one network to another without experiencing discontinuity of services. Indeed, MIPv6 protocol provides for continuous IP services to a mobile node (MN) by maintaining connectivity of the MN with the different networks. The mobile node is a mobile host such as, for example, a mobile phone, a laptop, a Personal Digital Assistant (PDA), etc.
The mobility services are deployed through a Home Agent (HA) which provides a Home Address (HoA) to a MN registered with that HA. When the MN moves away and attaches itself to a different access router, it acquires a new address, called the Care-Of Address (CoA). The MN then sends a Binding Update (BU) to the HA in order to bind the CoA to the HoA, so that traffic directed to the HoA is forwarded to the CoA. The HA replies back to the MN with a Binding Acknowledgement (BA) and forwards each data packet with HoA as destination address to the CoA using a bidirectional tunnel, for example. By so doing, the mobile node (MN) is able to move without ending ongoing sessions as the HoA of the MN remains unchanged.
However, there still exist mobile hosts that have not implemented MIPv6, for reasons such as they do not want to or they cannot. For those hosts, a proxy version, called PMIP, has been developed. When using IPv6, the proxy mobile IP is referred to as PMIPv6.
PMIP has been designed for local mobility handling. The MN is connected to an access router or Mobile Access Gateway (MAG) using a layer 2 access technology, for example. The MAG is responsible for managing the mobility at least partially on behalf of the MN. In a PMIP domain, a Local Mobility Anchor (LMA) is also defined for distributing the Home Network prefixes (or addresses) and hiding the mobility from the external world, i.e., outside of the PMIP domain. The binding is performed by the MAG using a Proxy BU (PBU) and the LMA responds back with a Proxy BA (PBA). When moving into the PMIP domain, the concept of CoA is replaced by a Proxy CoA (PCoA), which is the address of the MAG with which the MN is registered. Once the binding is completed, data packets are tunneled between the LMA and the MAG.
MIP offers global mobility and PMIP offers local mobility. More specifically, PMIP provides for network-based mobility management in the PMIP domain, i.e., the MAG manages the mobility at least partially on behalf of the MN. For this reason, it is common to see service operators using and deploying such PMIP domains.
It is now common to have mobile hosts with more than one network interface. In the contexts of MIP and PMIP, for instance, it is not always possible to ascertain which interface of a MN is to be used, especially when the MN is on the move from one access router to another.